Q: Is there a danger of owning too many individual stocks, say, 80 different stocks?

A: Moderation is often a good thing. And that age-old adage also applies to individual stocks.

Thanks to low-cost trading commissions, it's possible to build up a massive portfolio of dozens of individual stocks. But doing so offers little value to investors, and might actually be doing harm.

Keep in mind that while commissions at online brokers are low, usually $10 a trade or less, they can add up. Investors who added additional shares to just half their 80-stock portfolio, would rack up annual commissions of $400.

It's not just the cost. The power of diversification, or spreading an investment portfolio over many investments to protect against company-specific problems, loses its potency after a point. The number of stocks investors must own to stop getting a benefit is subject to debate.

One commonly held belief is that investors must have a 10-stock portfolio to be diversified. But another academic study showed at least 30 stocks are needed to be diversified.

Also, it's not the number of stocks that matters most, but the types of stocks. An investor might have a portfolio of 80 large U.S.stocks, and still not be diversified, since they lack investments overseas and in companies of different sizes.

Most likely, a portfolio with 80 individual stocks would be unwieldy and induce unnecessary costs. Investors who want to spread their money far and wide can do so at much lower costs. Low-cost exchange-traded funds allow investors to spread their money over hundreds of stocks in different asset classes.